What Is a Linear Module? A Practical Guide for Machine Builders
2025-11-281. What Is a Linear Actuator?
A linear actuator is a device that converts rotary motion (usually from an electric motor) into controlled linear motion — push, pull, lift, position, or press.
In practical engineering terms, a linear actuator gives you:
- A defined stroke (how far it moves)
- A controlled speed
- A certain force or thrust
- A way to mount it to your machine and attach your payload
Instead of designing all of this from scratch, you buy a standardized component that has been designed, tested, and rated by the manufacturer.
Common tasks for electric linear actuators include:
- Replacing pneumatic cylinders with more precise, programmable motion
- Moving tooling or fixtures into position
- Opening/closing doors, hatches, or covers
- Lifting or adjusting platforms
- Performing repeatable press or clamping operations
2. Main Types of Electric Linear Actuators
When people say electric linear actuator, they usually mean one of three core types:
- Ball screw actuator
- Belt drive actuator
- Direct-drive (linear motor) actuator
There are also rod-type electric cylinders, which are still screw- or belt-driven but packaged like a cylinder. For clarity, we’ll focus on the three main drive principles.
2.1 Ball screw actuator
A ball screw actuator uses a rotating ball screw and ball nut to convert rotary motion into linear motion.
- The screw is driven by a motor (stepper or servo).
- Recirculating balls inside the nut reduce friction and backlash.
- As the screw turns, the nut — and therefore the load — move linearly along the screw.
Key characteristics:
- High positioning accuracy and repeatability
- High stiffness and thrust for pushing/pressing
- Suitable for short to medium strokes
- Excellent for precision assembly, pick-and-place, testing, and pressing
2.2 Belt drive actuator
A belt drive actuator uses a timing belt looped around pulleys.
- The motor drives one pulley.
- The belt moves and pulls a carriage or slider along an aluminum body.
- The belt teeth mesh with the pulley to avoid slip.
Key characteristics:
- Very high speed and long stroke capability
- Lower stiffness and accuracy than a ball screw, but still very usable for many tasks
- Great for transfer, packaging, palletizing, loading/unloading, and any application where distance and speed matter more than micron-level accuracy
2.3 Direct-drive (linear motor) actuator
A linear motor actuator removes mechanical transmission elements entirely.
- Instead of a rotating motor plus screw or belt, it uses a linear motor coil and magnet track.
- The coil travels along the magnets, generating direct linear motion.
- Feedback comes from a high-resolution linear encoder.
Key characteristics:
- Excellent repeatability and no mechanical backlash
- Very fast acceleration and deceleration, ideal for short cycle times
- Higher system cost and requires more advanced control
- Used in semiconductor tools, high-speed inspection, laser processing, high-end assembly
3. Inside the Actuator: Working Principles
All electric linear actuators follow the same basic physics: a motor turns, and a mechanism converts that rotation into straight-line movement.
3.1 How a ball screw actuator works
- The motor (often with encoder) rotates the screw.
- The ball nut converts this rotation into linear travel via the helical groove and recirculating balls.
- Because balls roll rather than slide, friction is low and efficiency is high.
- The linear guide (rails and blocks) supports the moving carriage and load.
If you command 1 revolution of the screw, the nut advances by a distance equal to the screw lead. This gives a straightforward relationship between motor pulses and linear position.
3.2 How a belt drive actuator works
- The motor turns a toothed pulley.
- The timing belt, fixed to the carriage, moves as the pulley rotates.
- Linear guides keep the carriage and load aligned and supported.
Here, the relationship between rotation and travel is defined by the pulley circumference and belt tooth pitch. This setup allows very high speeds since there is no long rotating screw with critical speed issues.
3.3 How a linear motor actuator works
- The stator (usually containing permanent magnets) is fixed.
- The forcer/coil moves along the stator when energized.
- By precisely controlling the current in the coils, the controller generates a moving magnetic field that pulls the forcer along.
- A linear encoder measures position directly.
There is no transmission between motor and load, which means almost zero backlash and no mechanical wear from screws or belts. All motion performance depends on the controller, magnetic design, and machine structure.
4. Key Specs You Must Check
Regardless of type, every electric linear actuator is defined by a handful of important specifications. Understanding these specs is crucial if you want to choose the right product and avoid surprises.
4.1 Stroke (travel length)
- The maximum travel from one end position to the other.
- Must include the working range plus any home/over-travel margin.
- For ball screws, very long strokes may require screw support; for belts, you check belt sag and stiffness.
4.2 Load ratings
Actuators are rated for:
- Maximum permissible load (often in N or kg)
- Allowable moment loads (Mx, My, Mz) due to offset loads
You should consider:
- Static loads (weight of the tooling and product)
- Dynamic loads (inertia when accelerating and decelerating)
- How far the center of gravity is from the carriage (overhang → more moment)
Ignoring load and moment ratings can cause excess deflection, vibration, and premature wear.
4.3 Speed and acceleration
- Maximum speed is limited by screw critical speed, belt characteristics, or linear motor design.
- Maximum acceleration ties directly to the mechanical structure and motor/drive capability.
For example:
- A belt drive actuator might reach several meters per second.
- A ball screw actuator is usually slower but can offer better force and stiffness.
- A linear motor actuator can offer very high acceleration, but only if the machine frame is rigid enough.
Match these values to your cycle time and process requirements.
4.4 Thrust / force
- Ball screw actuators provide high continuous and peak thrust, ideal for pressing and pushing.
- Belt-driven actuators are more limited by belt strength and tooth shear.
- Linear motor actuators can deliver impressive peak force but may require active cooling or derating for continuous use.
Make sure the actuator’s thrust rating comfortably exceeds:
- The static load
- The dynamic force required to accelerate the load
- Any process forces (e.g., pressing, cutting, forming)
4.5 Accuracy and repeatability
Two related but different concepts:
- Positioning accuracy – the difference between the commanded position and the average actual position.
- Repeatability – how closely the actuator returns to the same position under identical conditions.
In many automation systems, repeatability matters more:
- Pick-and-place tools must land on the same pads or pockets every time.
- Dispensing paths must match the same tracks on every product.
Ball screw and linear motor actuators generally offer better repeatability than pure belt-driven axes, although belt systems can be accurate enough for many applications.
4.6 Stiffness and deflection
Stiffness determines:
- How much the system deflects under load
- How it behaves during high-acceleration moves
- Whether vibrations or oscillations appear at the tool
Stiffness depends on:
- The size of the linear guides
- The profile/housing geometry
- The mounting method and overall machine structure
It’s common to underestimate stiffness requirements, especially in vertical or cantilevered setups.
4.7 Environment and protection
Consider:
- Dust, chips, powders, or liquids
- Temperature range
- Cleanroom requirements
Suppliers usually offer:
- Semi-protected versions (open screw/belt with minimal covers)
- Fully enclosed versions (covers, bellows, or sealed housings)
Choosing the wrong protection level can dramatically shorten life in harsh environments.
5. Pros and Cons of Each Linear Actuator Type
A quick comparison to help in early design decisions:
Ball screw actuator
Pros
- High force and stiffness
- Good accuracy and repeatability
- Well suited for vertical and pressing applications
Cons
- Stroke length limited by critical speed of screw
- Rotating screw can generate noise at high speed
- More expensive than basic belt systems for long stroke
Belt drive actuator
Pros
- Long stroke with relatively low cost
- High speed capabilities
- Simple mechanical structure
Cons
- Lower stiffness and accuracy
- Belt stretch over time may require re-tensioning
- Not ideal for heavy pressing or very high precision
Linear motor actuator
Pros
- No screw or belt → no backlash from transmission
- Outstanding dynamic performance (speed, acceleration)
- Excellent repeatability with good encoder and controller
Cons
- Higher initial cost and more complex control
- Requires a stiff machine frame and careful design
- May need cooling or derating at high continuous loads
6. Practical Steps to Choose an Electric Linear Actuator
When specifying a linear actuator, follow a simple process:
- Define the motion task clearly
- Stroke, speed, acceleration, cycle time
- Load, orientation, process forces
- Required accuracy and repeatability
- Select the drive type
- If you need high force & precision → start with a ball screw actuator
- If you need long stroke & high speed at reasonable cost → start with a belt drive actuator
- If you need extreme dynamics & top-tier repeatability → evaluate a linear motor actuator
- Check the critical specs
- Load and moment capacity
- Speed and acceleration limits
- Thrust/force capability
- Expected lifetime and maintenance requirements
- Protection level for your environment
- Validate with the supplier’s data
- Use their load charts, deflection curves, and life calculations
- Request 3D models to check space and mounting
- Confirm motor and drive compatibility (stepper vs servo, feedback type, control interface)
7. Conclusion
When you strip away the jargon, a linear actuator is simply a tool to give your machine controlled straight-line motion. Understanding the differences between:
- Ball screw actuators
- Belt drive actuators
- Linear motor actuators
and knowing how to read their key specifications is what turns catalog pages into confident design decisions.
Next time someone asks for “linear actuator explained”, you’ll be able to move the conversation from vague product names to concrete requirements, trade-offs, and selections — exactly what a good machine builder needs.
